A homeless man used the last $20 in his pocket to buy gas for a stranded motorist because he feared for her safety — and what she did next changed his life.

Kate McClure, 27, and her boyfriend, Mark D’Amico, 38, made it their mission to get ex-Marine and firefighter Johnny Bobbit Jr. back on his feet with a fundraising campaign that has raised more than $65,000.

Bobbit came to McClure’s aid last month, when she ran out of gas on I-95 at night while driving to meet a pal in Philadelphia.

As she walked toward the nearest gas station, he told her to get back in her car and lock the doors.

Bobbit then spent his last $20 to buy her gas so she would get home safe.

“He came back and I was almost in shock,” McClure told The Post.

Bobbit asked for nothing in return — but McClure and her boyfriend stopped by his spot several times in recent weeks, repaying him for the gas money and dropping off clothes.

“We went to Target and got him a big backpack filled with stuff, and he opened the granola bars and offered us one,” she said. “We are like, ‘We just got this for you.’ He’s extremely generous.”

Touched by his selflessness, they started the fundraising campaign for Bobbit with a goal of $10,000 — enough to cover “first and last month’s rent at an apartment, a reliable vehicle, and 4 to 6 months worth of expenses.”

“This is nuts,” McClure said of the money they’ve raised through GoFundMe. “It has changed my entire outlook about people, my outlook about people has skyrocketed. It’s the best Thanksgiving that I’ve ever had.”

Bobbit is in “shock,” the couple said.

“We spoke to him yesterday, and it was around $17,000,” D’Amico said. “He kept saying I don’t want to waste this chance.

“We went from a room for four to six months, and now we are looking at apartments for the year,” D’Amico said.

And to their amazement, the money keeps pouring in for the 34-year-old Bobbit, a Marine Corps vet from North Carolina who also worked as a firefighter and paramedic before he fell on hard times.

“It’s like a $100 dollars a minute in the last half hour,” he said. “We got two separate $2000 donations. ”

“Some lady offered to pay his rent for a year,” D’Amico added.

The couple hopes Bobbit will join them for Thanksgiving dinner at McClure’s mom’s home.

“We are going to pick him up. Take him shopping,” D’Amico said.

Bobbit, who hails from North Carolina, has been homeless for a year and half, and began living under a bridge after he was robbed in a shelter.

“He came back from his service in the marines and for some reason it didn’t work out with his wife and it hit him hard,” D’Amico said. “He left North Carolina and started traveling around the United States.”

Bobbit wants to work at Amazon — and a recruiter from the tech giant has already reached out, saying she wants to help him get a spot.

“He’s a genuinely good guy so I think he deserves everything that’s coming to him,” McClure said.